A Fireproof, Lightweight, Polymer–Polymer Solid-State Electrolyte for Safe Lithium Batteries

Safety issues in lithium-ion batteries have raised serious concerns due to their ubiquitous utilization and close contact with the human body. Replacing flammable liquid electrolytes, solid-state electrolytes (SSEs) is thought to address this issue as well as provide unmatched energy densities in Li-based batteries. However, among the most intensively studied SSEs, polymeric solid electrolyte and polymer/ceramic composites are usually flammable, leaving the safety issue unattended. Here, we report the first design of a fireproof, ultralightweight polymer-polymer SSE. The SSE is composed of a porous mechanic enforcer (polyimide, PI), a fire-retardant additive (decabromodiphenyl ethane, DBDPE), and a ionic conductive polymer electrolyte (poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl)imide). The whole SSE is made from organic materials, with a thin, tunable thickness (10-25 μm), which endorse the energy density comparable to conventional separator/liquid electrolytes. The PI/DBDPE film is thermally stable, nonflammable, and mechanically strong, preventing Li-Li symmetrical cells from short-circuiting after more than 300 h of cycling. LiFePO₄/Li half cells with our SSE show a high rate performance (131 mAh g^-1 at 1 C) as well as cycling performance (300 cycles at C/2 rate) at 60 °C. Most intriguingly, pouch cells made with our polymer-polymer SSE still functioned well even under flame abuse tests.